1676, Charles Cotton, The Compleat Angler. Being Instructions how to Angle for a Trout or Grayling in a Clear Stream, London: Richard Marriott, and Henry Brome, OCLC228732346, March, page 59:

We have besides for this Month a little Dun call'd a whirling Dun (though it is not the whirling Dun indeed, which is one of the best Flies we have) and for this the dubbing must be of the bottom fur of a Squirrels tail and the wing of the grey feather of a Drake.

An ancient or medieval fortification; especially a hill-fort in Scotland or Ireland.

1858, Henry MacLauchlan, Memoir written during a survey of the Roman Wall, through the counties of Northumberland and Cumberland, in the years 1852-1854, London: Printed for private circulation, OCLC14866297, page 9:

Pampedun, or Pandon, was probably a place of residence from the earliest times; its sheltered situation for boats, and proximity to the ancient way over the river, protected perhaps by a dun or camp, on the height above [...] possibly gave origin to the ancient name of the place, Pampedun, from the British pant, a hollow, and dun, a fort or camp, Pant-y-dun.

(archeology) A structure in the Orkney or Shetland islands or in Scotland consisting of a roundhouse surrounded by a circular wall; a broch.

1832, James Thacher, History of Plymouth; from its first settlement in 1620, to the year 1832, Boston: Marsh, Capen & Lyon, OCLC78447431, page 317:

Dun-fish are of a superior quality for the table, and are cured in such a manner as to give them a dun or brownish color. Fish for dunning are caught early in spring, and sometimes February, at the Isle of Shoals.

English transcriptions of Mandarin speech often fail to distinguish between the critical tonal differences employed in the Mandarin language, using words such as this one without the appropriate indication of tone.